A trocar catheter is generally employed to penetrate an abdominal wall of a patient and can include a central stylet for the actual penetration and a surrounding tube through which gases and/or fluids may be injected or removed into or exhausted from the abdomen of the patient Frequently, also a protective tube or cannula is used to encompass the entire device to be inserted into the abdomen once penetration has occurred. Additionally various types of catheters and surgical instruments are manipulated through cannulas in endoscopic surgery.
A significant problem with catheters and surgical instruments, which have concentric, axial displaceable components, is to provide a seal between the components yet permit free axial displacement. A common solution to this problem is to provide some form of wiping seal or an inflatable collar which is expanded to fill the gap between such components. U.S. Pat. No. 4,932,959, issued Jun. 12, 1990, discloses an inflatable collar to this end used to release or secure a guide wire within a catheter. Also, U.S. Pat. No. 5,085,636 issued Feb. 4, 1992, discloses a balloon which is operative as an inflation and deflation valve to provide a fluid tight seal around a guide wire. In each instance, air pressure inflates an inflatable member which expands to occupy a space between components of the instrument. Such a mechanism is expensive, occupies considerable space, is not entirely reliable, and more importantly generates mechanical drag restricting free manipulation of the catheter.